By Weisburd, Stefi
Science News , Vol. 131
Washout at the GPS Shootout?
In the misty, early morning, a group in the park across fromSan Francisco's Civic Center huddled around two sets of strange-looking objects. The objects were radio wave antennas receiving satellite signals, and the people were scientists participating in the GPS Shootout: a competition among four companies developing receivers for the Global Positioning System (GPS). The GPS is the Department of Defense's multi-billion-dollar navigation system, which for a few million dollars more will enable civilian scientists to measure distances of several kilometers to within less than a centimeter.
Because it measures distances between two ground stationsby comparing the times it takes for radio signals to arrive from a satellite, the GPS is not limited, as are most other surveying and navigation methods, by the curvature of the earth. "GPS has turned the surveying world inside out," says John D. Bossler, director of the Center for Mapping at Ohio State University in Columbus. Scientists studying the movement of the plates and the deformation of the crust say GPS will be less expensive, faster and provide more information about height differences of ground stations than existing methods. …